WASHINGTON (CNN) -- President Obama on Monday gathered together every confirmed member of his Cabinet for the first time as president and challenged them to cut $100 million in the next 90 days.

President Obama meets Monday with his Cabinet, including Defense Secretary Robert Gates, right.

Agencies will have to report how they saved on expenses at the end of the period.

The federal government has "a confidence gap when it comes to the American people," Obama said at the White House.

"We've got to earn their trust. They've got to feel confident that their dollars are being spent wisely."

The edict is part of Obama's "commitment to go line by line through the budget to cut spending" and "reform the government," a senior administration official said.

One potential Cabinet officer was missing from the meeting -- Kansas Gov. Kathleen Sebelius, the health and human services secretary-designate. The Senate has not voted on whether to confirm Sebelius to the post.

Obama made his savings request as the House of Representatives and Senate were returning from recess this week, ready to start reconciling their versions of the fiscal 2010 budget resolution. The president's budget request is $3.67 trillion. Watch how the administration hopes to cut costs »

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In the context of the federal budget, $100 million in savings is a small amount, critics said.

"Any amount of savings is obviously welcome," Senate Minority Leader Mitch McConnell, R-Kentucky, said. "But [$100 million is] about the average amount we'll spend every single day just covering the interest on the stimulus package that we passed earlier this year."

White House press secretary Robert Gibbs insisted that ordinary Americans nevertheless would appreciate the savings effort.

"Only in Washington, D.C., is $100 million not a lot of money," Gibbs said. "It is where I'm from. It is where I grew up. And I think it is for hundreds of millions of Americans."

The administration also contends the order signaled an important demonstration of fiscal responsibility.

"None of these savings by themselves are going to solve our long-term fiscal problems," Obama said. "But taken together, they can make a difference, and they send a signal that we are serious about how government operates."

The White House offered examples of how agencies already have started cost-cutting measures, including:

The Department of Homeland Security's plan to save an estimated $52 million over five years by purchasing office supplies in bulk.

The Department of Agriculture's effort to consolidate 1,500 employees from seven locations into a single facility in 2011. Such a move has been estimated to save $62 million over a 15-year lease.

The Department of Veterans Affairs will cancel or delay 26 conferences, saving nearly $17.8 million. The department also will use video-conferencing to cut costs.

A Department of Education decision to increase the ratio of people using each printer is anticipated to save an additional $6.7 million. Cutting the ratio of computers per employee is expected to save another $2 million.